1. Field of the Invention
The present invention relates to a digital recording apparatus, such as a DVD (digital video disc) recording/reproduction apparatus and a digital VCR, and a digital recording method. In particular, this invention is concerned with such digital recording apparatus and method that can effectively prevent unauthorized copying that is not intended by a creator or producer of data, while limitedly permitting digital copying.
2. Prior Art
Conventionally, a digital data transmission system has been proposed, in which digital recording/reproduction apparatuses, such as optical disc (e.g., DVD) reproduction apparatus, digital TV, digital VCR, and others, are connected to each other via an IEEE-1394 bus that serves as an intelligent interface, so that data contents, such as pictures and music, are transmitted and received between these digital apparatuses. When digital data is transmitted and received between these apparatuses, the system checks if each of the apparatuses operates in a manner as intended by the creator or producer who created the contents of the data, and, if any apparatus does not operate as intended by the creator, data transfer is prohibited, to thereby prevent the user from illegally copying the picture and/or music contents against the intention of the creator.
Digital main data to be transmitted contains copy control information called xe2x80x9cCCIxe2x80x9d. The CCI consists of two bits, namely, xe2x80x9c00xe2x80x9d, xe2x80x9c10xe2x80x9d or xe2x80x9c11xe2x80x9d, where xe2x80x9c00xe2x80x9d indicates permission of free copying, xe2x80x9c10xe2x80x9d indicates permission of one-time copying, and xe2x80x9c11xe2x80x9d indicates prohibition of copying.
Upon transmission of digital data, the transmitter-side apparatus initially checks the CCI to determine its copy restriction level for the contents of the digital data, and also checks, on the IEEE-1394 bus, whether the receiver-side apparatus operates in a manner as intended by the content creator. If complete authentication is established between the receiver-side apparatus and the transmitter-side apparatus, the contents is encrypted and transmitted from the transmitter-side apparatus. In this case, where the CCI information of the digital data transmitted from the transmitter-side apparatus is, for example, xe2x80x9c10xe2x80x9d, and the receiver-side apparatus is a sound recording apparatus, the CCI is rewritten into xe2x80x9c11xe2x80x9d and thus recorded during copying of the digital data. As a result, second and subsequent copying actions are prohibited, and thus only one-generation copying is realized.
As another method for preventing unauthorized copying by digital picture apparatuses, it has been proposed to use electronic watermark information (generally called xe2x80x9cwatermarkxe2x80x9d). In this method, watermark information may be directly added to a non-obvious or low-intensity portion of the waveform of a picture signal, or may be embedded into a particular frequency component of frequency conversion information of the original signal. By providing the watermark with information on permission/prohibition of copying, the watermark is able to indicate whether free copying is permitted, or only reproduction of the data is permitted, for example.
While the above description is related to the system using a digital transmission line called IEEE-1394 bus, the contents to be recorded is also often transmitted through an ordinary analog signal transmission line, to a digital recording apparatus. In this case, too, it is naturally desirable to employ a digital recording method that effectively prevents unauthorized copying that is not intended by the data producer or creator while limitedly permitting digital copying.
The conventional system using the digital bus, however, has not taken account of the case where picture/music signals are transmitted in the form of analog signals to a digital recording apparatus. In the case of digital recording of data transmitted in the form of analog signals, matching of the analog signal transmission with the system using the digital bus has not been taken into consideration.
When the known digital recording apparatus receives digital broadcasting waves containing CCI for copy restriction, and rewrites the CCI from xe2x80x9c10xe2x80x9d (indicating permission of one-time copying) into xe2x80x9c11xe2x80x9d (indicating prohibition of copying), for example, it is relatively easy to rewrite xe2x80x9c10xe2x80x9d into xe2x80x9c00xe2x80x9d (indicating permission of free copying) through two-bit manipulation, thus causing a problem that unauthorized copying may be done without difficulty.
In the method using watermarks, on the other hand, watermark information is distributed over a relatively wide range of picture and/or voice information contained in main data of digital data to be transmitted, and it is therefore difficult for the receiver-side apparatus to rewrite this information. If the watermark information is to be rewritten on the user level, the receiver-side apparatus needs to be provided with a considerably large circuit. This is advantageous over the use of CCI in terms of prevention of unauthorized or illegal copying. However, since the watermark cannot be easily rewritten as described above, it is rather difficult to permit one-time copying by rewriting or changing the flag (i.e., watermark) as in the case where CCI is used.
To make up for the impossibility or difficulty of rewriting of watermarks, an attempt has been made to introduce the concept of media marks that are incorporated into only original contents, but not generated or output to reproduced signals. It is, however, technically difficult to incorporate such marks into analog signals, and it is also rather difficult to introduce the concept into such media as digital broadcasting, which have been already put into practice.
It is therefore an object of the present invention to provide a digital recording apparatus and a digital recording method that are able to prevent unauthorized digital copying more effectively, while allowing the use of different forms or levels of copy restriction, in a system that transmits analog signals or digital broadcasting waves.
To attain the above object, according to a first aspect of the present invention, there is provided a digital recording apparatus that receives an analog signal containing at least one of picture and voice information, through an analog transmission line, and digitally records the analog signal, comprising an electronic watermark information detecting device that detects presence and content of electronic watermark information contained in a first portion of the received analog signal comprising the at least one of picture and voice information, the electronic watermark information indicating permission of free copying or prohibition of copying, a recording device that digitally records the analog signal received through the analog transmission line, and a control device that controls the recording device so as to allow the recording device to digitally record the analog signal in a form containing the electronic watermark information within the first portion of the analog signal while adding copy control information indicating permission of free copying to a second portion of the analog signal that does not include the at least one of picture and voice information when the electronic watermark information detected by the electronic watermark information detecting device indicates permission of free copying, prohibit the recording device from digitally recording the received analog signal when the electronic watermark information detected by the electronic watermark information detecting device indicates prohibition of copying, and allow the recording device to digitally record the received analog signal while adding copy control information indicating prohibition of subsequent recording to the second portion of the analog signal when no electronic watermark information is detected by the electronic watermark information detecting device.
To attain the above object, according to a second aspect of the present invention, there is provided a digital recording apparatus connected to a receiver system that receives a digital broadcasting wave signal containing at least one of picture and voice information, for digitally recording the digital broadcasting wave signal received by the receiver system, comprising an electronic watermark information detecting device that detects presence and content of electronic watermark information contained in a first portion of the digital broadcasting wave signal comprising the at least one of picture and voice information, the electronic watermark information indicating permission of free copying or prohibition of copying, a copy control information determining device that determines a content of copy control information that indicates a copy restriction level, the copy control information being contained in a second portion of the received digital broadcasting wave signal that does not include the at least one of picture and voice information, and a recording device that digitally records the received digital broadcasting wave signal, and a control device that controls the recording device so as to digitally record the received digital broadcasting wave signal in a form containing the electronic watermark information and the copy control information, according to the copy restriction level determined by the copy control information determining device when the electronic watermark information indicating permission of free copying or prohibition of copying is detected by the electronic watermark information detecting device, and digitally record the received digital broadcasting wave signal in a form containing the copy control information, according to the copy restriction level determined by the copy control information determining device when the electronic watermark information detecting device detects no electronic watermark information in the received digital broadcasting wave signal.
Preferably, the copy control information indicates one of copy restriction levels representing permission of free copying, permission of one-generation copying, and prohibition of copying.
In a preferred form of the second aspect, the control device controls the recording device such that the recording device digitally records the received digital broadcasting wave signal along with the electronic watermark information and the copy control information both indicating permission of free copying when the electronic watermark information detected by the electronic watermark information detecting device indicates permission of free copying and the copy restriction level determined by the copy control information determining device indicates permission of copying, the recording device digitally records the received digital broadcasting wave signal along with the electronic watermark information while changing the copy control information into that indicating prohibition of copying when the electronic watermark information detected by the electronic watermark information detecting device indicates prohibition of copying and the copy restriction level determined by the copy control information determining device indicates permission of one-generation copying, and the recording device is inhibited from digitally recording the received digital broadcasting wave signal when the electronic watermark information detected by the electronic watermark information detecting device indicates prohibition of copying and the copy restriction level determined by the copy control information determining device indicates prohibition of copying.
In another preferred form of the second aspect, the control device controls the recording device such that the recording device digitally records the received digital broadcasting wave signal without electronic watermark information while containing the copy control information indicating permission of copying when no electronic watermark information is detected by the electronic watermark information detecting device and the copy restriction level determined by the copy control information determining device indicates permission of copying, the recording device digitally records the received broadcasting signal without electronic watermark information while changing the copy control information into that indicating prohibition of copying when no electronic watermark information is detected by the electronic watermark information detecting device and the copy restriction level determined by the copy control information determining device indicates permission of one-generation copying, and the recording device is inhibited from digitally recording the digital broadcasting wave signal when no electronic watermark information is detected by the electronic watermark information detecting device and the copy restriction level determined by the copy control information determining device indicates prohibition of copying.
To attain the above object, the present invention also provides a digital recording method of receiving an analog signal containing at least one of picture and voice information, through an analog transmission line, and digitally recording the analog signal, comprising the steps of detecting presence and content of electronic watermark information contained in a first portion of the received analog signal comprising the at least one of picture and voice information, the electronic watermark information indicating permission of free copying or prohibition of copying, digitally recording the received analog signal in a form containing the electronic watermark information within the first portion of the analog signal while adding copy control information indicating permission of free copying to a second portion of the analog signal that does not include the at least one of picture and voice information when the electronic watermark information detected in the step of detecting electronic watermark information indicates permission of free copying, inhibiting digital recording of the received analog signal when the electronic watermark information detected in the step of detecting electronic watermark information indicates prohibition of copying, and digitally recording the received analog signal while adding copy control information indicating prohibition of subsequent recording to the second portion of the analog signal when no electronic watermark information is detected in the step of detecting electronic watermark information.
To attain the above object, the present invention further provides a digital recording method of digitally recording a digital broadcasting wave signal that is received by a receiver system, the digital broadcasting wave signal containing at least one of picture and voice information, comprising the steps of detecting presence and content of electronic watermark information contained in a first portion of the received digital broadcasting wave signal comprising the at least one of picture and voice information, the electronic watermark information indicating permission of free copying or prohibition of copying, determining copy control information that indicates a copy restriction level and is contained in a second portion of the received digital broadcasting wave signal that does not include the at least one of picture and voice information, and digitally recording the received digital broadcasting wave signal in a form containing the electronic watermark information and the copy control information, according to the copy restriction level determined in the step of determining copy control information when the electronic watermark information indicating permission of free copying is detected in the step of detecting electronic watermark information, and digitally recording the digital broadcasting wave signal in a form containing the copy control information, according to the copy restriction level determined in the step of determining copy control information when no electronic watermark information is detected in the received digital broadcasting wave signal in the step of detecting electronic watermark information.
In the digital recording apparatus and method according to the present invention, no matter whether picture and/or voice information is received in the form of an analog signal, or in the form of a digital signal received as digital broadcasting waves, electronic watermark information that is difficult to rewrite is included in a portion of the signal comprising the picture and/or voice information, so that copy restriction designated by the watermark information can be imposed in accordance with the intention of the contents supplier. The digital recording apparatus freely performs copying operations when the electronic watermark information indicates permission of free copying, and at the same time adds copy control information indicating permission of free copying to the signal. When the electronic watermark information indicates prohibition of copying, the apparatus is inhibited from copying or recording the received signal. If no electronic watermark information is detected, which is interpreted as permitting only one-generation copying, the recording apparatus records the received signal, while adding copy control information indicating prohibition of copying, to the recorded signal. While the copy control information may be easily rewritten, this information is recorded along with the electronic watermark information that is difficult to rewrite where any electronic watermark information is detected. Thus, subsequent copying will be prohibited even if the copy control information were rewritten with some intention.
The above and other objects, features, and advantages of the invention will become more apparent from the following detailed description taken in conjunction with the accompanying drawings.